The art of hydrocarbon conversion, such as the cracking of petroleum fractions employing catalysts in fluid processes, is well established. The more recent types of catalyst for such purpose have been the crystalline alumino silicate catalysts. One widely used form of such catalysts is the microspheres produced by spray drying a slurry containing a zeolite, clay and alumina. They have been formulated by spray drying a slurry containing particles of the catalyst combined with a matrix comprising alumina hydrates. (See Secor U.S. Pat. No. 3,445,727 and art cited therein.) Examples of such catalysts are those formulated by spray drying a slurry containing a zeolite of the faujasite type, preferably a Y zeolite. (See Breck U.S. Pat. No. 3,130,007), which has been exchanged with monovalent cations, for example, NH.sub.4 or polyvalent cations such as rare earth cations to reduce the sodium content in the range of about 1% to about 4%. For example, such zeolites are combined in a water slurry with a kaolin clay and with hydrated alumina.
It has been shown in the prior art that pseudoboehmite is a desirable form of hydrated alumina for use in the matrix for the zeolite Y containing hydrocarbon conversion catalyst to produce a catalyst of suitable attrition resistance and catalytic activity for use in fluid cracking systems. The zeolite component may range from about 10% to about 50%, the alumina from about 5% to 50% and the clay from about 20% to about 85%, all on a volatile free basis. The slurry is spray dried to form particles referred to as microspheres, for example, having an average nominal diameter in the range of about 50 to about 70 microns.
Alumina hydrate may be formed from an aluminum sulfate by hydrolysis with ammonium hydroxide as is well known (see Kehl et al, U.S. Pat. No. 3,188,174) or from ammonium alum (See Secor Patent supra.)
It is recognized in this art that not all alumina hydrates including all forms of pseudoboehmites are equally useful for such purpose (see Secor, et al, U.S. Pat. No. 4,010,116, Lim et al U.S. Pat. Nos. 4,086,187, and 4,206,085.
As has been shown in the above Lim, et al, patent and Lim et al, applications, the Attrition Index of an exchanged zeolite containing kaolin clay, and a suitable form of pseudoboehmite is considerably improved, if the slurry which is spray dried to give microspheres contains some ammonium polysilicate.
In our copending application Ser. No. 06/138,544 filed Apr. 9, 1980, we have shown that the conversion of aluminum sulfate into a suitable pseudoboehmite is uniquely different from the conversion of the aluminum salt of a monovalent strong acid such as AlCl.sub.3 or Al(NO.sub.3).sub.3 in that pseudoboehmites produced by the procedure which results in a suitable pseudoboehmite from the monovalent acid salts by the procedure of that application is not suitable for the sulfate salt. See also Kehl et al U.S. Pat. No. 3,188,174 and Secor et al and Lim et al patents, supra.
As described in the above patents and patent applications, convenient tests have been developed which select pseudoboehmites suitable for incorporation in the catalysts containing exchanged Y and a matrix referred to above. The details of the test which is referred to in this specification are described in our copending application which application is incorporated in this application by this reference.
The test develops a Peptization Index (PI) as the time in minutes required for a pseudoboehmite peptized by formic acid to develop a Brookfield Viscosity of 5000 centipoises.
14.9 grams of the pseudoboehmite (on a volatile free basis) is dispersed in sufficient water to weigh 145 grams. To this water slurry is added 1.4 grams of 90% formic acid and the slurry is stirred until the vortex disappears. The slurry is then incorporated promptly into a Brookfield viscosimeter and the interval of time measured until the viscosity reaches 5000 centipoises. Time is measured from the time that the formic acid is added to the slurry.
The Peptization Index of the test alumina hydrate is the number of minutes required to reach the above viscosity. (A pseudoboehmite which fails to arrive at the above viscosity in sixty (60) minutes is unlikely to reach such viscosity at even a greatly prolonged period of time.) The alumina hydrate of our invention, which is produced by the process of our invention is characterized by a Peptization Index of sixty (60) or less than sixty (60) minutes.
The test procedure for determining the Attrition Index (AI) of spray dried microspheres of the catalyst referred to in this specification is described in the aforesaid Secor, et al U.S. Pat. No. 4,010,116.
The test procedures by which the catalytic activity of the catalyst in which the alumina produced according to our invention is described in our copending application Ser. No. 06/138,544.
The test procedure for determining the pore size distribution, pore volume and surface area of the alumina of our invention is described in the copending application incorporated herein by this reference.